11.3 Properties of Liquids

11.3 Properties of Liquids

By: Mira Amin, Katie Blackburn, Neil Marfatia

Viscosity

• Viscosity – the resistance of a liquid to flow – Stronger the intermolecular

forces, greater the viscosity slower it flows

– Common unit = poise (P) = 1 g/cm-s

• Usually reported in centipoise (cP) = .01 P

• Depends on attractive forces b/w molecules – Viscosity increases with

molecular weight– Viscosity decreases with

temperature

Surface Tension

• Molecules at the surface experience net inward force– Pulls molecules from

surface into interior lowers surface area

– Packs molecules closer together

• Surface Tension – energy required to increase the surface area of a liquid by a unit amount (units: J/m^2)– Stronger the

intermolecular forces, higher the surface tension

– Water has high surface tension b/c of strong hydrogen bonds

Allows water striders to “walk” on water

Coin floats on waterA soap bubble balances surface tension forces against internal pneumatic pressure.

Dew forming on a leaf

Surface Tension • Cohesive forces –

intermolecular forces that bind similar molecules to one another– Ex: hydrogen bonding in

water• Adhesive forces –

intermolecular forces that bind a substance to a surface – Ex: formation of a

meniscus • Capillary action – rise of

liquids up very narrow tubes– Helps water and

dissolved nutrients travel upward through plants

Capillary Action

Chapter Questions

• 1) How do viscosity and surface tension of liquids change as intermolecular forces become stronger? – b) as temperature increases?

• 2) Distinguish between adhesive forces and cohesive forces – b) explain the cause for the U-shaped

meniscus formed when water is in a glass tube

– c) how is the capacity of paper towels to absorb water related to capillary action?

Chapter Answers

• Higher viscosity and surface tension– As temp. increases, viscosity and

surface tension decrease

• Cohesive forces bind similar molecules together, while adhesive forces bind a substance to a surface– Meniscus forms b/c adhesive forces b/w

H2O and glass are greater than cohesive forces b/w H2O molecules

– Liquid adheres to the paper towel

Bibliography

• http://www.metacafe.com

• http://www.science.uwaterloo.ca/~cchieh/cact/c123/liquid.html

• http://ga.water.usgs.gov/edu/capillaryaction.htm

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• http://palimpsest.stanford.edu/don/dt/dt3713.html

• http://www.fas.harvard.edu/~scdiroff/lds/NewtonianMechanics/CapillaryAction/

CapillaryAction.html